The present invention relates to the production of native gp160 of human immunodeficiency virus (HIV), the etiologic agent of Acquired Immune Deficiency Syndrome (AIDS).
Human Immunodeficiency Virus (HIV) is now well established as the etiological agent of acquired immunodeficiency syndrome (AIDS). The virus is tropic for cells bearing the CD4 antigen and is highly cytopathic for helper-inducer (T4) cells. The envelope gene product of HIV is synthesized as a gp160 precursor molecule, which is subsequently processed into the external envelope protein gp120 and the transmembrane protein gp41. The precursor/product relationship between gp160 and the smaller proteins, gp120 and gp41, has now been well documented, as well as the amino acid sequences of all three [Allan, et al., Science, 228:1091-1094 (1985) and Veronese, et al, Science, 229:1402-1405 (1985)]. The external glycoprotein gp120 binds to the CD4 molecule on susceptible cells in the initial phase of viral cell fusion and giant cell formation induced by the virus [Dalgleish, et al., Nature, 312:763-766].
In addition to their role in cell surface receptor recognition and cell fusion, HIV gp120 and gp41 are the primary targets for immune recognition in individuals infected with HIV. Hence, these proteins have received special attention in virus neutralization studies and vaccine development. It has been observed that large segments of gp120 expressed by recombinant DNA techniques, or native gp120 purified from HIV-infected cells, elicit mostly type-specific neutralizing antibodies in animals. In addition, the HIV envelope precursor protein gp160 expressed in insect cells with baculovirus vectors produced a strong type-specific immune response in goats [Rusche, et al., PNAS, USA 84:6924-6928 (1987)].
The ability to infect certain cell lines with HIV, and to establish the infected cells into a continuous producer of intact virus has been described in U.S. Pat. No. 4,652,599. Even the ability to infect the cell line and the HIV variant of the present invention have been previously described [Getchell, et al., J. Clin. Microbiol. 23:737-742 (1986)].
However, neither of these events alone permitted the establishment of a process capable of producing the HIV glycoprotein gp160 in its native form. Normally, native gp160 breaks down into gp120 and gp41. Consequently, the envelope protein obtained from cell culture media or from lysed virus is gp120 and gp41. It is therefore most surprising that gp160 may be obtained in its native form.
Glycoprotein gp160 has only been produced through recombinant means. However, recombinant gp160 is different than the native gp160, particularly in regard to glycosylation. These differences become critical in the search for an HIV vaccine, particularly since the envelope glycoproteins of HIV determine viral tropism and harbor epitopes which are essential for the development of neutralizing antibodies against the virus.